Chapter 15: Visualizing the Atom
Losing Valence Electrons
The shell model described in Section 15.4 can be used to explain a wide variety of
properties of atoms. Using the shell model, for example, we can explain how atoms
within the same group tend to lose (or gain) the same number of electrons. Let's
consider the case of three group 1 elements: lithium, sodium, and potassium. Look to
a periodic table and find the nuclear charge of each of these atoms:
Nuclear
charge:
Number of
i nner shell
electrons:
+3
+11
10
2
+19
18
How strongly the valence electron is held to the nucleus depends on the strength of the
nuclear charge-the stronger the charge, the stronger the valence electron is held. There's
more to it, however, because inner-shell electrons weaken the attraction outer-shell electrons
have for the nucleus. The valence shell in lithium, for example, doesn't experience the full
effect of three protons. Instead, it experiences a diminished nuclear charge of about +1. We
get this by subtracting the number of inner-shell electrons from the actual nuclear charge.
What do the valence electrons for sodium and potassium experience?
Diminished
nuclear
charge:
~+1
~+1
~+1
Question: Potassium has a nuclear charge many times greater than that of lithium. Why
is it actually easier for a potassium atom to lose its valence electron than it is
for a lithium atom to lose its valence electron?
Potassium's valence electron is much
farther from the nucleus. Because the
electric force decreases with distance, the
+1 charge for potassium's valence electron
is not so effective at holding to the atom.
Hence, it is easily lost.
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